1. Field of the Invention
The present invention relates to an image forming apparatus, and more particularly, to an electrophotographic color image forming apparatus.
2. Description of the Related Art
Generally, an electrophotographic image forming apparatus prints a desired image in a manner that a toner is supplied to a photosensitive medium where an electrostatic latent image is formed, to form a toner image. The toner image is then transferred to a printing paper. Meanwhile, the electrophotographic color image forming apparatus forms a visible color image on the photosensitive medium by developing the electrostatic latent image formed on the photosensitive medium by supplying four colors of toners consecutively.
FIG. 1 shows an example of a conventional electrophotographic color image forming apparatus.
Referring to FIG. 1, the conventional color image forming apparatus includes a photosensitive drum 10 having a layer to be electrically charged and generating an electric potential difference at an electrically charged area when the layer is exposed to a light source, a charging unit 20 to electrically charge the photosensitive drum 10, a laser scanning unit 30 to convert an electric signal of image data to be formed to an optical signal and projecting the converted signal to the photosensitive drum 10 such that the electrostatic latent image is formed on the photosensitive drum 10 by the electric potential difference. A developing unit 40 in the conventional color image forming apparatus develops the electrostatic latent image by supplying toners of different colors consecutively, a transferring unit 50 transfers the toner image formed on the photosensitive drum 10 to the printing paper P, a fusing unit 60 fixes the toner image to the printing paper P and a paper feeding unit 70 feeds the printing paper P.
The developing unit 40 includes four developers 42, 43, 44, and 45 to develop the electrostatic latent image of the photosensitive drum 10 by supplying the photosensitive drum 10 with toners of yellow, magenta, cyan, and black, consecutively. The respective developers 42, 43, 44, and 45 include toner containers 46 to contain the color toners, developing rollers 47 to supply the color toners contained in the toner containers 46 to the electrostatic latent image area of the photosensitive drum 10, and gap rings 48 to maintain gaps between the developing rollers 47 and the photosensitive drum 10. Also, the respective developers 42, 43, 44, and 45 are disposed along a circular turret 41 with a distance apart from one another, and they close to the photosensitive drum 10 one by one, consecutively, when the turret 41 rotates to develop the electrostatic latent image of the photosensitive drum 10 with the respective color toners.
The transferring unit 50 includes a transfer belt 51 as a moving medium by which the toner mage formed on the photosensitive drum 10 is carried, a first transfer roller 52 to transfer the toner image from the photosensitive drum to the transfer belt 51, and a second transfer roller 53 to transfer the toner image from the transfer belt 51 to the printing paper P.
The conventional electrophotographic color image forming apparatus, as constructed above, forms the electrostatic latent image on the photosensitive drum 10 by projecting a laser beam from the laser scanning unit 30 into the photosensitive drum 10, which is electrically charged to a predetermined electric potential by the charging unit 20.
Subsequently, the electrostatic latent image is developed by the developing unit 40. Typically, the respective developers 42, 43, 44 and 45 approach the photosensitive drum 10 by an order of yellow, magenta, cyan and black as the turret 41 rotates to develop the electrostatic latent image. At this point, when the developing roller 47 of one developer approaches the photosensitive drum 10 with the gap with respect to the photosensitive drum 10, the toner is jumped onto the photosensitive drum 10 by an electrostatic force that is generated by the electric potential difference between the photosensitive drum 10 and the developing rollers 47. The developing roller 47 can maintain the gap with respect to the photosensitive drum 10 using the pair of gap rings 48 disposed at both sides of the developing roller 47.
Visible color images formed on the photosensitive drum 10 by the above develop processing are overlapped on the transfer belt 51, and the image on the transfer belt 51 is transferred to the printing paper P passing between the transfer belt 51 and the second transfer roller 53.
The printing paper P where the image is transferred, passes through the fusing unit 60 to fix the image to the printing paper P and then, the printing paper P is fed out.
However, the conventional electrophotosenstive color image forming apparatus has a problem of noise caused due to the developing unit 40 that is operated using a developer moving method. That is, when the respective developers 42, 43, 44, and 45 approach the photosensitive drum 10 as the turret 41 rotates, the gap rings 48 of the developers come into contact with a surface of the photosensitive drum 10 causing the noise problem.
Also, a shock occurs when the gap rings 48 of the developers come into contact with the photosensitive drum 10, which is transferred to the photosensitive drum 10, thereby deteriorating the toner image formed on the photosensitive drum 10 to be transferred from the photosensitive drum 10 to the transfer belt 51. Accordingly, a problem of image quality deterioration occurs in the conventional electrophotsensitive color image forming apparatus.